private void discoverBackEdges(DiGraphNode<N, E> u) {
u.setAnnotation(GRAY);
for (DiGraphEdge<N, E> e : u.getOutEdges()) {
if (ignoreEdge(e)) {
continue;
}
DiGraphNode<N, E> v = e.getDestination();
if (v.getAnnotation() == WHITE) {
discoverBackEdges(v);
} else if (v.getAnnotation() == GRAY) {
e.setAnnotation(BACK_EDGE);
}
}
u.setAnnotation(BLACK);
}
